parametes for guluronic acid residues

Dear all,
I want to do a cg MD simulation of Ca-alginate hydrogel using Martini.
Although, Martinni provides, paramters for different carbohydrate moeoties, I didnt find the paramters for alginate residues [poly-D-guluronic acid]

Can any one let me know how to get the paramters for this guluronic acid and simulate..